Many people are uncomfortable in bright sunlight without sunglasses. Since prescription spectacles are relatively expensive, it has become common to provide tinted “clip-on” auxiliary lenses to enable the use of one pair of prescription spectacles indoors and out. Initially such “clip-ons” were mechanically attached to the parent spectacles as by hooks or other mechanical means, but recently magnetic attachment has become popular. Examples of magnetic attachment schemes can be found in many prior art patents.
A first group of prior art patents is exemplified by Chao, U.S. Pat. No. RE37,545, Madison, U.S. Pat. No. 6,149,269, Zelman, U.S. Pat. No. 6,343,858, Kwok, U.S. Pat. No. 6,116,730 Nishioka, U.S. Pat. No. 5,642,177 and Cate, U.S. Pat. No. 6,164,774. This first group is characterized by an auxiliary lens attachment having a construction very much like that of the spectacles to which it attaches, but instead of having temples, the attachment has a pair of magnet-containing-arms, each magnet mating with a corresponding magnet affixed to one of the endpieces of the parent spectacles. Depending on the patent, the magnets are disclosed as facing in some particular direction, e.g. upward, downward, forward, rearward or outward.
A second group of patents is represented by Sadler, U.S. Pat. No. 5,416,537. Instead of locating magnets on external arms, Sadler's style of attachment involves embedding magnets in the temporal portions of the auxiliary lens structure itself. These embedded magnets face rearward, and mate with corresponding magnets embedded in the parent spectacle frame.
A third prior art group is illustrated by Starner et al., U.S. Patent Application Publication No. 2002/0089639. The Starner disclosure describes a plurality of small magnets attached to each auxiliary lens near its periphery. Each attached magnet mates with a corresponding magnet attached to the frame of the parent spectacles.
Finally, a fourth group is represented by Meeker, U.S. Pat. No. 4,070,103 and McKenna et al., U.S. Pat. No. 6,412,942. These patents teach the use of continuous magnetic bands. In Meeker, a continuous magnetic band surrounds the spectacle rim. In McKenna et al. the eyewire of each auxiliary lens is fabricated from a spinodal decomposition alloy which, when heat treated, becomes a permanent magnet that is attracted to the magnetically permeable rim of the parent spectacles.